This invention relates generally to gravity blenders and more particularly to improvements for gravity blenders which are connected to pressurized discharge systems.
In the past, it has been known to connect a gravity blender with a pressurized discharge system such as a fluid current conveyor. Fluid current conveyors quickly and efficiently move blended particulate material from the blender, where the material may be stored, to other areas of a plant for use or other processing.
Typically, the gravity blender includes an elongated bin having several conduits therein that convey particulate material downwardly from selected regions of the bin under the influence of gravity. These conduits normally discharge particulate material into a blending zone where the material is intermixed.
In applications where the blending zone empties particulate material into a pressurized discharge system, a pressure differential often occurs between the interior of the bin and the blending zone. Such pressure differentials are undesirable since they may cause pressure-induced holdup of the particulate material. The holdup results from a resistance to downward gravity-induced movement of particulate material which is generated by a high pressure from below that is opposed by a lower pressure from above.
In gravity blender applications where the discharge zone does not empty into a pressurized discharge system, a pressure-induced material holdup can also result simply from the displacement of particulate material from a closed bin. As particulate material leaves the bin the volume available to air trapped therein increases and causes a sub-atmospheric internal pressure. Thus material flowing by gravity from a closed bin to atmospheric pressure again may be resisted by a pressure differential.
The pressure-induced product holdup leads to intermittent or unsteady flow from the blender which makes volumetric flow rates from the blender difficult to accurately predict and control.
Further, with many finely divided particulate materials that are gravity blended and discharged to atmospheric systems, undesirable quantities of dust may escape causing both waste and pollution.
As a consequence, it would be desirable to have a gravity blender substantially free from the above undesirable characteristics. It is to be noted however, that indiscriminate positioning of apparatus within a gravity blender may result in substantially adverse effects on the operation thereof. Accordingly, this invention relates to a method and apparatus for solving the problems in a direct and efficient manner.